The present application relates to an inhaler for delivery of medicament from a canister, in particular to an actuation mechanism for actuating the canister held in the inhaler.
Inhalers are commonly used to deliver a wide range of medicaments. The inhaler holds a canister of medicament which is actuatable, for example by compression, to deliver a dose of medicament. Some known inhalers are provided with an actuation mechanism for actuating the canister. The mechanism may be breath-actuated, ie. arranged to actuate the canister in response to inhalation at the mouthpiece. Typically a breath-actuated inhaler includes a loading mechanism for loading a resilient loading element with an actuation force for compression of the canister. A triggering mechanism may be provided to hold the resilient loading element against compression of the canister, the triggering mechanism releasing the resilient loading element upon inhalation.
In such an actuation mechanism the resilient loading element must provide a sufficiently high force to compress the canister. In general, the force generated by a resilient loading element decreases as it expands during the compression stroke of the canister. For example if the resilient loading element is a spring, the force generated will decrease linearly with the expansion of the spring in proportion to its spring constant. Therefore, to provide sufficient force at the end of the compression stroke of the canister, the force generated by the resilient loading element at the beginning of the stroke is larger still. This is the loaded position in which the actuation mechanism will usually be stored, ready for use.
However, it is undesirable to store the actuation mechanism with the resilient loading element applying a high force to the other elements holding the loading element in its loaded position, such as the triggering mechanism. This is because the high force can cause creep in the various components subject to the high force, particularly if the components are made of plastic which is desirable to reduce costs and simplify manufacture. Over time such creep can distort the components of the actuation mechanism. This can have the effect of causing improper actuation of the canister, for example by causing actuation at an incorrect inhalation flow or, in the worst case, preventing operation of the actuation mechanism at all.
According to the present invention, there is provided an inhaler for delivery of medicament from a canister which is compressible to deliver a dose of medicament, the inhaler comprising:
a housing for holding a canister;
a canister engagement member engageable with a canister held in the housing to compress the canister;
a loading mechanism for loading a resilient loading element which is arranged, when loaded, to bias the canister engagement member to compress the canister;
a triggering mechanism arranged to hold the canister engagement member against compression of the canister and triggerable to release the canister engagement member,
wherein the linkage between the resilient loading element and the canister engagement member is arranged to reduce the force applied by the canister engagement member to the triggering mechanism when held by the triggering mechanism.
The present invention is based on the appreciation that it is possible to arrange the linkage between the resilient loading element and the canister engagement member to reduce the force above other canister engagement members and to the triggering mechanism in the loaded state. There are many different ways of arranging the linkage to achieve this.